Today, as high integration of large-scale integrated circuits (ICs) has been accompanied by a need for a fine circuit pattern, semiconductor microfabrication process technology has emerged as a very important issue. In the case of a highly integrated circuit, circuit wires become finer for low power consumption and high-speed operations, and there is a growing need for a contact hole pattern for an interlayer connection and a circuit arrangement for high integration. Thus, in order to satisfy such demands, a photomask on which an original circuit pattern is recorded needs to be manufactured to be finer and to be capable of recording a more precise circuit pattern thereon.
A photolithography technology has been developed to shorten an exposure wavelength by using a 436 nm g-line, a 365 nm i-line, 248 nm KrF laser, or 193 nm ArF laser in order to improve the resolution of a semiconductor circuit pattern. However, the shortening of the exposure wavelength greatly contributes to an improvement on the resolution of a semiconductor circuit pattern but deteriorates a depth of focus (DoF), thereby increasing a burden on design of an optical system including a lens. Accordingly, in order to solve this problem, a phase-shift mask has been developed to improve both the resolution and DoF of a semiconductor circuit pattern using a phase-shift layer that shifts the phase of exposure light by 180 degrees.
A conventional phase-shift mask is manufactured by sequentially forming a light-shielding film and a resist film pattern on a phase-shift layer, forming a light-shielding film pattern by etching the light-shielding film using the resist film pattern as an etch mask, and etching the phase-shift layer using the light-shielding film pattern as an etch mask. The light-shielding film should have a predetermined optical density so as to effectively block light. To this end, the light-shielding film may be formed to a thickness of about 600 or more. In this case, a resist film may be formed to a thickness of about 2,000 or more so as to etch the light-shielding film, based on the thickness of the light-shielding film.
Recently, as patterns have become finer and higher denser, for example, to have a size of 45 nm or less, and particularly, 32 nm or less, a photomask is required to be manufactured to have not only a high resolution but also precise critical dimension (CD) mean-to-target (MTT), CD uniformity, and CD linearity.
However, since a conventional phase-shift mask uses a resist film having a thickness of about 2,000 or more, a fine resist film pattern is difficult to form. Thus, it is difficult to form a fine light-shielding film pattern that is used as an etch mask for etching a phase-shift layer, thereby preventing manufacture of a fine phase-shift layer pattern.
Accordingly, there is a growing need to develop a new blankmask, the optical density of which can be maintained at about 2.0 to 4.0, and that allows a resist film to be formed to a thin thickness, thereby improving CD characteristics.